1. Field of the Invention
The present invention relates to a broadband wireless access system. More particularly, the present invention relates to an apparatus and method for generating a command for power control in a broadband wireless access system.
2. Description of the Related Art
According to UpLink (UL) power control prescribed by the High Speed Packet Access (HSPA) standard, a Base Station (BS) transmits a Transmit Power Control (TPC) command to a terminal every slot and, according to the TPC command, the terminal increases or decreases a UL transmit power by one level. In detail, the BS compares a Signal-to-Noise Ratio (SNR) of a receive signal with a reference value. In a case where the SNR is less than the reference value, the BS transmits a TPC command to increase a transmit power and, in a case where the SNR is greater than the reference value, the BS transmits a TPC command to decrease the transmit power, thereby guaranteeing reception performance irrespective of a changing channel environment and efficiently managing power consumption of the terminal.
The reference value, which is a value for guaranteeing reception performance despite a changing channel environment, is determined in an upper layer of a system on the basis of current reception performance. For example, the reception performance is maintained in a way of, if demodulation of a receive signal has succeeded, the reference value is decreased and, if demodulation fails, the reference value is increased. The guaranteed reception performance varies according to the amount the reference value is decreased or increased.
Generally, a Wideband Code Division Multiple Access (WCDMA) system of the related art employs a rake receiver, so a power control scheme of the related art has been optimized for the rake receiver. Accordingly, a BS calculates an SNR on the assumption that a receive signal is processed by the rake receiver, compares the SNR with a reference value for guaranteeing reception performance of the rake receiver, and controls a transmit power of a terminal. Power control of the related art is carried out in a unit of one slot (i.e., 0.667 millisecond (ms)) that is a basic unit of power control as prescribed in the HSPA standard. A packet for a WCDMA service, i.e., a voice service is basically composed of a frame of a length of 10 ms, and one frame is composed of 15 slots. That is, according to the power control scheme of the related art, transmit power control is carried out 15 times during an interval of one frame.
In a case of a High Speed Uplink Packet Access (HSUPA) service, i.e., a data service, a more optimal reception method is employed in which processing is performed with an equalizer rather than a rake receiver to thereby achieve a high data rate and the like. The rake receiver allocates fingers to multi-path components, respectively, and demodulates each of the multi-path components. The equalizer performs demodulation after eliminating a multi-path component, leaving only a single-path component. Accordingly, an output SNR when receiving the same receive signal passing through a multi-path by the rake receiver and an output SNR when receiving the same by the equalizer are different from each other.
As described above, power control of the related art is carried out on the premise of a rake receiver. However, because an SNR which is used as a reference of power control is different according to the kind of the receiver, there is a need to present an alternative for performing effective power control by changing a power control scheme adaptively according to the kind of receiver employed.